1. Field of the Invention
This invention relates to a method for separating fractions of urban refuse which has been incinerated, and/or fractions of industrial refuse of a similar kind, the purpose being to recuperate these fractions with a high recuperation yield without having to use special equipment.
2. Description of the Prior Art
Several prior methods are known for sorting out various fractions from urban or industrial refuse in order to extract magnetic and non-magnetic metals and the mineral fraction. However, these methods require costly investments and entail a large energy consumption, which is inherent to these methods. One very simple method is also known, which consists in passing the refuse through a percussion crusher-shredder, but it will only allow extracting ferrous scrap by magnetic separation and by comminuting the non-magnetic fraction to a grain size from 0 to 50 mm, this latter fraction being used after screening as a road-fill material or for underbed drainage in road-building. Thus, while this method requires only a small investment with moderate operating costs, it presents the major drawback of being able to concentrate solely magnetic metals.
A further handling of the non-magnetic fraction available from the magnetic separator may be considered, but experience shows that this fraction, with a grain size from 0 to 50 mm, does not lend itself, in any possible manner, to the recuperation of non-magnetic metals, nor to the extraction of glass wastes, nor to the reuse of slag in the production of earthenware, since every attempt towards this entails the addition of expensive equipment with a large and costly energy consumption.
As for the other methods, they provide for a better recuperation of the various fractions, but their operation costs are high, in addition to which they have the drawback of operating solely either through a dry process or through a wet process.
Two main cases are known at present.
In the first case, after screening out the coarser fractions, when required, the fractions passing through the sieve are dried, if needed, before undergoing a selective crushing along three successive stages in which the slag is pulverized and metals are shredded and flattened. The metals are then extracted by screening and by magnetic and gravimetric separations. This method requires a thorough elimination of dust and does not properly suit the nature of the product treated because incinerated refuse must be either sprayed with water or immersed in a water-filled tank to be extinguished and extracted from the kilns. Therefore, if the clinker is too damp, the drying operation becomes costly, or else, if it is too dry, dust removal must be carried out at many locations. Moreover, this method leaves no possibility for washing away the soluble salts contained in the ashes, the presence of which is detrimental to the production of earthenware products from these ashes.
In the second case, all the various fractions, metallic or other, of the incinerated refuse are effectively separated, but this is at the cost of a large number of operations, so that the stations where the various concentrates are produced are widely spread apart, which requires considerable handling and reworking of the refuse. Also, all the operations are exclusively "wet process" operation, which results in an excessive consumption of water at the screening stations and to an unavoidable repetition of operations for draining water out of the pulp and for repeated pulping.
Thus, there does not exist at present any method for sorting out the various fractions contained in incinerated urban refuse or in industrial refuse of similar nature, without consuming too much power, particularly where the clinker is too damp when it is to be treated by a dry process, or otherwise too much water is consumed when all the operations are "wet process" operations.